This invention relates to an electromagnetic valve device having two electromagnetic valves, which is adapted for use e.g. in antiskid control brake systems for automotive vehicles.
An electromagnetic valve device of this kind has been proposed e.g. by British Patent Publication No. 1428741, which comprises a first electromagnetic valve comprising a first hollow cylindrical member (tubular section), a first winding wound on the first hollow cylindrical member, a first core which is slidable within the first hollow cylindrical member by energization or deenergization of the first winding, and a first return spring urging the first core, a second electromagnetic valve comprising a second hollow cylindrical member (tubular section), a second winding wound on the second hollow cylindrical member, a second core which is slidable within the second hollow cylindrical member by energization or deenergization of the second winding, and a second return spring urging the second core, and a cap made of a ferromagnetic material and forming part of magnetic paths associated with the first and second cores, the first and second electromagnetic valves being arranged in superposed coaxial relationship and housed within the cap with a ferromagnetic disc-shaped member interposed therebetween.
This conventional electromagnetic valve device is presumably assembled in the following manner: the component parts of the first and second electromagnetic valves are incorporated one by one into the cap through an open end thereof, and then a closing member is screwed into the open end of the cap to complete the assembly work. Therefore, in this electromagnetic valve device, lots of component parts of the two electromagnetic valves have to be incorporated into a single cap, which makes the assembly work complicated and time-consuming, thus being unsuitable for mass production of the electromagnetic valve device.
Further, the conventional electromagnetic valve device is a three-way valve for fluid in which energization and deenergization of each winding of the two valves is controlled to thereby cause each core to slide by the magnetically attracting force of the winding associated therewith to open and close each valve to thereby selectively establish communication between three fluid passages. In this valve device, the duration and timing of opening/closing of each electromagnetic valve is electrically controlled by a pulse signal applied to each winding. However, with such electrical control of the opening/closing of two electromagnetic valves, there is a possibility that the valves are not positively opened or closed at desired timing due to variations in frictional forces acting on the core of each valve etc. For example, one valve does not open following closing of the other valve, but the one valve can open even while the other valve is still open. This results in a undesired state of communication between the three fluid passages.
In the meanwhile, an assembly unit having a plurality of electromagnetic valve devices, which is used in antiskid control brake systems, has been proposed by Japanese Provisional Patent Publication No. 63-96378 (corresponding to German Patent Application No. P 36 34 349.8). The assembly unit comprises a plurality of electromagnetic valve devices, a base member having pairs of first and second fluid passages corresponding in number to the number of the electromagnetic valve devices and disposed such that communication between each pair of first and second fluid passages is controllably established or cut off by each electromagnetic valve device associated therewith, a magnetic hollow cylinder-forming element having a plurality of magnetic hollow cylinders integrally formed therewith and accommodating each electromagnetic valve, and a covering plate, wherein the electromagnetic valves and magnetic hollow cylinder-forming element are clamped between the base member and the covering plate to form a changeover valve assembly unit.
However, according to this prior art, when assembling the changeover valve assembly unit, it is required that the electromagnetic valve devices be placed onto the base member at respective separate predetermined locations, and then the magnetic hollow cylinder-forming element be placed onto the base member such that each magnetic hollow cylinder accommodates each magnetic valve device associated therewith. This imposes problems of many assembly steps and complicated assembly works. Further, in this prior art, the magnetic hollow cylinders of the magnetic hollow cylinder-forming element are formed of a magnetic material, since they each serve as a frame for forming magnetic paths for each electromagnetic valve device, as well as a frame for holding each associated electromagnetic valve. Therefore, each magnetic hollow cylinder adversely affects magnetic attracting forces generated by electromagnetic valve devices which are accommodated in respective adjacent magnetic hollow cylinders.